Here's the symptom: you're on a Claude Max plan, your usage dashboard says you've barely touched your quota, and yet Claude Code is billing your requests to extra usage — the pay-as-you-go credits on top of your plan. One user watched $200 in extra usage charges pile up while his plan quota sat at 86% unused.
The trigger sounds like something I made up to get views. It isn't.
If any recent commit message in your git repository contained the exact case-sensitive string HERMES.md, Claude Code routed your API requests to extra usage billing instead of your plan quota. Lowercase hermes.md didn't trigger it. HERMES without the extension didn't either. One add HERMES.md commit was enough.
What was actually happening
This is issue #53262 on the Claude Code repo, filed on 25 April 2026 with full repro steps. It collected 92 comments, and it's one of the rare bug reports that got a same-day answer from Anthropic. Boris Cherny, who leads Claude Code, replied:
"Thanks for the report! This was an overactive anti-abuse system. Fixed."
So the mechanism wasn't billing code reading your filenames. It was an anti-abuse classifier — something watching for patterns associated with abuse — that decided HERMES.md in commit history was one of those patterns, and quietly downgraded those sessions from plan quota to metered billing. Nobody outside Anthropic knows why that particular string was on the list, and they haven't said.
Five days later, Anthropic's Thariq Shihipar followed up with the part that matters for your wallet:
"We're reaching out to affected users and giving them a refund + another month of credits (in this case another $200). You should get an email soon if you were affected."
Confirmed, fixed server-side, refunds issued. That's about as good as bug resolution gets.
What to do now
The fix landed on Anthropic's side in late April 2026, so there's nothing to patch locally. What's left is checking whether it cost you money:
- Open your Anthropic billing page and look for extra usage charges from April 2026 — especially any period where your plan quota wasn't close to exhausted.
- Search your repos for the trigger:
git log --all --oneline | grep "HERMES\.md". A hit plus unexplained extra usage charges in that window means you were probably affected. - If you find charges and never got the refund email, contact Anthropic support and reference issue #53262. They were proactively refunding — a missed case with evidence is an easy conversation.
One caveat worth knowing: a user commented on 21 May — a month after the fix — saying he could still reproduce it. The issue was already closed and locked, so that report went nowhere. I couldn't reproduce it on v2.1.202. If you see plan-quota requests landing in extra usage today, file a fresh issue and link the old one.
What not to do
The advice floating around the threads at the time was to rewrite your git history — git filter-branch or an interactive rebase to scrub the string out of old commits. Don't.
It was already questionable advice when the bug was live (rewriting shared history breaks every teammate's clone, to dodge a bug Anthropic needed to fix anyway). After the server-side fix, it's pure cost with zero benefit. Your commit history is fine. Leave it alone.
The receipts
- Issue #53262 — closed as completed, 25 April 2026. Anthropic-confirmed: the maintainer quotes above are in the thread.
- The "$200 while 86% quota sat unused" figure comes from the original reporter — one user's account, not an Anthropic number.
- Verified against Claude Code v2.1.202 on 7 July 2026.
The bigger lesson: when your billing looks wrong, check the issue tracker before you assume you misread your own usage. This one sounded too weird to be real. It was real, and it paid out refunds.
More fixes like this, before they hit the blog